Strange cloacal/vent display

I have been noticing that everytime I take my bino male out of his cage his vent is open. Looks almost like hes gonna go poo or something but nothing comes out. Coukd this be a sign of wanting to breed? I havent thrown him in with any girls because he is still pretty small maybe 4-450g. I am just wondering if anyone else has seen this before. THanks. Will be eagerly awaiting replies lol. :D

I have also noticed this a few times with my mojo.

I take it no one has experienced this. Its not really a big deal I just thought it was weird and couldnt find anything on the web about it.